Messages in this thread | | | Date | Fri, 4 Aug 2023 09:59:04 +0300 | Subject | Re: [PATCH v5 4/7] perf record: Track sideband events for all CPUs when tracing selected CPUs | From | Adrian Hunter <> |
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On 4/08/23 05:07, Yang Jihong wrote: > User space tasks can migrate between CPUs, we need to track side-band > events for all CPUs. > > The specific scenarios are as follows: > > CPU0 CPU1 > perf record -C 0 start > taskA starts to be created and executed > -> PERF_RECORD_COMM and PERF_RECORD_MMAP > events only deliver to CPU1 > ...... > | > migrate to CPU0 > | > Running on CPU0 <----------/ > ... > > perf record -C 0 stop > > Now perf samples the PC of taskA. However, perf does not record the > PERF_RECORD_COMM and PERF_RECORD_MMAP events of taskA. > Therefore, the comm and symbols of taskA cannot be parsed. > > The solution is to record sideband events for all CPUs when tracing > selected CPUs. Because this modifies the default behavior, add related > comments to the perf record man page. > > The sys_perf_event_open invoked is as follows: > > # perf --debug verbose=3 record -e cpu-clock -C 1 true > <SNIP> > Opening: cpu-clock > ------------------------------------------------------------ > perf_event_attr: > type 1 (PERF_TYPE_SOFTWARE) > size 136 > config 0 (PERF_COUNT_SW_CPU_CLOCK) > { sample_period, sample_freq } 4000 > sample_type IP|TID|TIME|CPU|PERIOD|IDENTIFIER > read_format ID|LOST > disabled 1 > inherit 1 > freq 1 > sample_id_all 1 > exclude_guest 1 > ------------------------------------------------------------ > sys_perf_event_open: pid -1 cpu 1 group_fd -1 flags 0x8 = 5 > Opening: dummy:u > ------------------------------------------------------------ > perf_event_attr: > type 1 (PERF_TYPE_SOFTWARE) > size 136 > config 0x9 (PERF_COUNT_SW_DUMMY) > { sample_period, sample_freq } 1 > sample_type IP|TID|TIME|CPU|IDENTIFIER > read_format ID|LOST > inherit 1 > exclude_kernel 1 > exclude_hv 1 > mmap 1 > comm 1 > task 1 > sample_id_all 1 > exclude_guest 1 > mmap2 1 > comm_exec 1 > ksymbol 1 > bpf_event 1 > ------------------------------------------------------------ > sys_perf_event_open: pid -1 cpu 0 group_fd -1 flags 0x8 = 6 > sys_perf_event_open: pid -1 cpu 1 group_fd -1 flags 0x8 = 7 > sys_perf_event_open: pid -1 cpu 2 group_fd -1 flags 0x8 = 9 > sys_perf_event_open: pid -1 cpu 3 group_fd -1 flags 0x8 = 10 > sys_perf_event_open: pid -1 cpu 4 group_fd -1 flags 0x8 = 11 > sys_perf_event_open: pid -1 cpu 5 group_fd -1 flags 0x8 = 12 > sys_perf_event_open: pid -1 cpu 6 group_fd -1 flags 0x8 = 13 > sys_perf_event_open: pid -1 cpu 7 group_fd -1 flags 0x8 = 14 > <SNIP> > > Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
> --- > tools/perf/Documentation/perf-record.txt | 3 ++ > tools/perf/builtin-record.c | 44 +++++++++++++++++++++++- > 2 files changed, 46 insertions(+), 1 deletion(-) > > diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt > index 680396c56bd1..dac53ece51ab 100644 > --- a/tools/perf/Documentation/perf-record.txt > +++ b/tools/perf/Documentation/perf-record.txt > @@ -388,6 +388,9 @@ comma-separated list with no space: 0,1. Ranges of CPUs are specified with -: 0- > In per-thread mode with inheritance mode on (default), samples are captured only when > the thread executes on the designated CPUs. Default is to monitor all CPUs. > > +User space tasks can migrate between CPUs, so when tracing selected CPUs, > +a dummy event is created to track sideband for all CPUs. > + > -B:: > --no-buildid:: > Do not save the build ids of binaries in the perf.data files. This skips > diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c > index 3ff9d972225e..e575b5e295a2 100644 > --- a/tools/perf/builtin-record.c > +++ b/tools/perf/builtin-record.c > @@ -908,10 +908,44 @@ static int record__config_off_cpu(struct record *rec) > return off_cpu_prepare(rec->evlist, &rec->opts.target, &rec->opts); > } > > +static bool record__tracking_system_wide(struct record *rec) > +{ > + struct record_opts *opts = &rec->opts; > + struct evlist *evlist = rec->evlist; > + struct evsel *evsel; > + > + /* > + * If all (non-dummy) evsel have exclude_user, > + * system_wide is not needed. > + * > + * all_kernel and all_user will overwrite exclude_kernel and > + * exclude_user of attr in evsel__config(), here need to check > + * all the three items. > + * > + * Sideband system wide if one of the following conditions is met: > + * > + * - all_user is set, and there is a non-dummy event > + * - all_user and all_kernel are not set, and there is > + * a non-dummy event without exclude_user > + */ > + if (opts->all_kernel) > + return false; > + > + evlist__for_each_entry(evlist, evsel) { > + if (!evsel__is_dummy_event(evsel)) { > + if (opts->all_user || !evsel->core.attr.exclude_user) > + return true; > + } > + } > + > + return false; > +} > + > static int record__config_tracking_events(struct record *rec) > { > struct record_opts *opts = &rec->opts; > struct evlist *evlist = rec->evlist; > + bool system_wide = false; > struct evsel *evsel; > > /* > @@ -921,7 +955,15 @@ static int record__config_tracking_events(struct record *rec) > */ > if (opts->target.initial_delay || target__has_cpu(&opts->target) || > perf_pmus__num_core_pmus() > 1) { > - evsel = evlist__findnew_tracking_event(evlist, false); > + > + /* > + * User space tasks can migrate between CPUs, so when tracing > + * selected CPUs, sideband for all CPUs is still needed. > + */ > + if (!!opts->target.cpu_list && record__tracking_system_wide(rec)) > + system_wide = true; > + > + evsel = evlist__findnew_tracking_event(evlist, system_wide); > if (!evsel) > return -ENOMEM; >
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